Override devices are already known, in particular for certain hydraulic flight controls and in particular for pitch control surfaces, that enable the pilot to take over from the electric motor which in normal operation actuates the hydraulic circuit of the control.
FIG. 1 is a diagram of a control unit comprising a hydraulic control valve 1, an electric motor 2, and an override device 3.
The valve 1 is actuated in normal operation by the electric motor 2, which in turn is controlled by a flight control computer.
The override device 3 enables the pilot to take over from the electric motor 2 and the computer and to impose manual control on the pitch control surface, in particular by acting on control means 4.
FIGS. 2a and 2b are diagrams showing an override device which is presently in use with the pitch control surfaces of certain airplanes.
The device 3 comprises:
an outlet gear 5 which meshes with complementary means of the hydraulic control valve 1;
an inlet gear 6 which lies on the same axis as the gear 5 and which meshes with complementary means of a transmission system driven by the electric motor 2;
an intermediate assembly 7 which is interposed between the two gears 5 and 6 and lies on the same axis; this assembly 7 is rotated by the inlet gear 6; it has a set of fluting 8a which co-operates with complementary fluting 8b on the outlet gear 5 so that in normal operation the inlet gear 6 drives the outlet gear 5 via said intermediate assembly 7; and
a shaft 9 lying on the axis of the gears 5 and 6 and of the intermediate assembly 7; this shaft 9 carries a gear 10 which co-operates with complementary means of a transmission system enabling the actuator means 4 to drive said shaft 9; it also includes a plate 11 having a cam 12 against which there bears a cam follower 13 carried by the intermediate assembly 7; it also includes abutment-forming means represented by a fork 17 in FIGS. 2a and 2b, enabling the shaft 9 to rotate the gear 6 when the pilot acts on the shaft 9.
Particularly when the pilot acts on the shaft 9 via the means 4, the cam follower 13 runs along the cam 12 so that the intermediate assembly 7 is pushed back from the gear 5. The complementary fluting 8a, 8b uncouples. The outlet gear 5 is no longer driven by the electric motor 2. Rotation of said gear 5 is then controlled by the pilot causing abutments represented by the fork 17 to come into abutment, thereby controlling the movement which is imparted to the pitch control surface via the hydraulic system.
Provision is also made for the intermediate assembly to include a set of friction disks 14, with the friction disks being brought into engagement with one another by compression from a helical spring 15 interposed between said assembly 7 and said gear 6 when the cam-follower means 13 move over the cam 12 and the intermediate assembly 7 is pushed back towards the inlet gear 6. These sets of friction disks then enable a certain amount of friction to be maintained between the gears 5 and 6 throughout the time that manual control is being applied, however the gear 6 does not drive the gear 5 unless the pilot releases the force exerted on the inlet shaft 9 via the means 4.
The intermediate assembly also carries pusher means which act on switches I to activate a given signal inside the cockpit when the pilot acts on the manual control means and the intermediate assembly is displaced.
Nevertheless, an override device of the type described above is expensive to make.
An object of the invention is to propose a structure for an override device which is simplified and less expensive to make.
Another object of the invention is to propose a structure for an override device which provides manual control giving the pilot control sensations that are similar to those of a conventional manual control.
Thus, the invention provides an override device, in particular for flight controls, comprising a manual control part, an inlet gear part, and an outlet gear part which are mounted to rotate about the same axis, means being interposed between the inlet gear part and the outlet gear part so that in normal operation the inlet gear part rotates the outlet gear part, the manual control part also carrying a cam which, in co-operation with complementary means of an intermediate part suitable for following said cam, serves to disengage the means interposed between the inlet gear part and the outlet gear part under the effect of torque exerted on the manual control part, the device also having means then enabling the manual control part to drive the outlet gear part.
In the device proposed by the invention the drive means interposed between the inlet gear part and the outlet gear part comprise a set of friction disks and spring means suitable for exerting a force to compress said disks against one another, and the intermediate part suitable for following the cam carries at least one pusher-forming element which, at the end of a displacement of the intermediate part relative to the cam under drive from torque exerted on the manual control part exerts force opposing that of the spring means and relaxes the friction force on at least some of the disks.
Such a device is simplified in structure compared with the structure described with reference to FIGS. 2a and 2b: in particular, it does not require parts to be manufactured having drive fluting; the outlet part is driven by the inlet part via the set of friction disks.
Furthermore, the number of parts is smaller.
Such a device is advantageously associated with the various characteristics below taken singly or in any technically feasible combination:
the intermediate part includes abutment-forming means which, at the end of a displacement of the intermediate part relative to the cam under drive from torque exerted on the manual control part, come to bear against at least one complementary surface of the outlet part, the manual control part then driving the intermediate part and the outlet part;
a portion of the friction disks has a bearing zone against which the pusher-forming element comes to bear at the end of a displacement of the intermediate part relative to the cam; in this way, the inlet part always opposes the torque exerted by the pilot on the manual control part by means of a force of opposite sign which is transmitted thereto via the friction disks that remain in engagement, from the pusher-forming element and the intermediate part; this friction is important insofar as it provides the pilot with reaction relative to which the pilot can adjust the force applied;
the other friction disks have a recess passing through them to allow the pusher-forming element to be displaced;
the set of friction disks comprises a plurality of carbon disks alternating with metal disks;
the set of friction disks includes at least five carbon disks;
the pusher-forming element comes to bear against two disks of the set of friction disks;
the intermediate part carries two cam-follower wheels which run on the cam;
the wheels have axles constituting pins suitable for coming to bear against complementary surfaces of the outlet part;
the axles of the wheels constitute pins which are engaged in a cylindrical part slidably mounted in a sheath which extends the manual control part along its axis, said cylindrical part being driven to slide relative to said sheath when the intermediate part moves relative to the cam and constituting a pusher suitable for controlling the switching of at least one switch; and
the device includes a helical spring which is interposed coaxially between the intermediate part and the outlet part and which provides return displacement of the intermediate part relative to the cam when the force on the manual control part is released.